Infants who experience chronic malabsorption and malnutrition in the first two years of life become short, growth-retarded children who may experience irreversible central nervous system and intellectual impairment. Therefore, it is critical that nutritional intervention begin early so that optimal nutritional needs of the HIV-infected infants are met. Furthermore, early nutrition intervention may help reduce the susceptibility to or severity of primary HIV as well as opportunistic infections and add to quality of life for perinatally HIV-infected children. The purpose of this study is to evaluate the effect of concentrated infant formula compared with standard infant formula on weight gain, body composition, immunologic and virologic status, quality of life, and dietary intake in HIV-infected infants from birth to 6 months.